I have a huge Gmail inbox. I'm not one of those people who archive email once it's "done". I spam report every spam I get. I rarely delete anything. Wasn't that the original Gmail pitch?
As a result a pet hate of mine is when my inbox claims there are some unread mail messages when I know the first two pages of email are completely read.
The usual suspect? Spam. Spam that's been given an absurd date.
One of my gripes is that Gmail doesn't suspect Russian email (or any email!) dated to 1977 could be spam. Sure. Email dated to 1997 could be a fresh import of inbox data... but not 1977.